This invention relates to water-sealed type vacuum pumps and more specifically, to a vacuum pump in which a pump is connected to a suction pipe and air is sucked and exhausted by suction and discharge actions of a liquid tank.
Vacuum pumps which have heretofore been used in vacuum drying apparatus include vapor ejector pumps, oil rotating vacuum pumps, and water-sealed type vacuum pumps. In the case of the vapor ejector pump, a multi-stage ejector must be used to obtain a carry-over pressure as desired and a great amount of vapors are used up, naturally resulting in an increase of drying cost. In the case of the oil rotating pump, the vapor is sucked and hence the performance is materially lowered such as by deterioration of oil and decrease in exhaust velocity. In order to eliminate these drawbacks, the pump and oil tank are heated by vapor or electrical heat to excessively heat the vapor into a non-condensed gas, which is discharged to prevent water from being mixed with the oil. In the conventional water-sealed type vacuum pumps, the carry-over pressure as desired cannot be obtained even if the circulating water temperature should be decreased to about 5.degree. C., with the result that the low temperature vacuum drying could not be accomplished. Further, conventional vacuum pumps suffer from various disadvantages. For example, since deaerating is accomplished while directly sucking and exhausting air itself to be deaerated, it is extremely difficult to obtain a high degree of vacuum due to the presence of mechanical clearance of the pump. Also lubricating oil is emulsified with the water content under suction to hamper the lubricating action. Also if entry of a large amount of water is made during suction, phenomena such as water hammer and knocking occurs and a cumbersome starting operation is involved.